The field of the invention is in the preparation of concrete forms, specifically, in the preparation of the separator (expansion joint) inserted prior to the pouring of two adjacent concrete sections. The present invention is placed upon the expansion joint prior to the pour, and remains anchored to the concrete to cover the expansion joint once the concrete has cured.
Concrete used for pedestrian or vehicular traffic must be separated into slabs to accommodate many factors such as shrinkage during cure, environmental changes, aging, and uneven settling over years of service. Large areas are divided into slabs through the use of wood, fiber-board, or similar ‘forms’, which are used primarily for their convenience and low cost, rather than for aesthetic or maintenance considerations. These forms are left between slabs after curing, and are sometimes referred to as ‘expansion joints’.
Prior art consists of two techniques to finish and seal concrete expansion joints. These two methods can be divided into cure-in-place liquid sealants, and covers applied over the forms, and left in-place.
Use of liquid sealants, while the most common method, has several drawbacks. A space for them must be created by the removal of a portion of the form after some period of concrete cure. This secondary operation must be performed with the consideration of many environmental factors which may be detrimental to the performance of the sealant: precipitation, or the likelihood thereof, a proper temperature for the curing of the material, the presence of wind-blown debris during the pour and cure, and the control of traffic or other disturbance during the cure of the sealant.
The second, newer method consists of form covers applied before the pour, which cover the top of the forms, such that after the pour, only the cover is visible. The first example, shown in FIG. 11, has a pair of arrow-shaped features to preclude the removal of the cover from the form after the pour. This example, however, fails to allow for the eventual rot and disappearance of the form. With the disappearance of the form, this cover can collapse inward, and will then be free to be removed or driven into the gap. Additionally, any motion of the slabs tending to increase the space between the slabs will cause separation between the slab and the form cover. This allows the intrusion of water, seed and debris, which will allow weeds and grasses to occupy this space. The present invention addresses this by providing anchoring features that will keep the compliant trim attached to the concrete, whether or not the forms are present. Additionally, the present invention will tolerate movement of the slabs, while still maintaining a seal with the concrete.
One additional example is shown in FIG. 12. This cover provides ample features for the anchoring of the cover to the concrete slab. It fails to account for the weakening of the slab that such features will create, nor does it properly consider the slump angle of the concrete. Wet concrete is a thick fluid, with a natural angle of repose, or ‘slump’ angle. During the pour, it will be difficult to force the concrete into the spaces below the anchoring features, necessitating a vibratory action to try to get the concrete to settle and hopefully fill the undercut areas. As these areas are invisible, it is almost impossible to verify that all these spaces are filled, and that the slab is void-free. The present invention acknowledges this angle, and does not contain features which would be difficult to engage during the pour. It should be noted, however, that even if a void-free pour were attained, the compressive strength of the form cover, being many orders of magnitude less than concrete, will not support the concrete above it. As a result, as in the case of a void, a cantelever of concrete that is significantly weaker than the rest of the slab is produced at the expansion joints. In practice these areas have been observed to crack and fail prematurely.
While both of these cited examples have their strengths and weaknesses, they both share an additional critical weakness, in that they do not address axial shrinkage of the cover. Flexible plastic materials contain plastisizing agents which continue to evolve from the material over their lifetime. This results in shrinkage of the material, which is typically only noticed over long lengths. The examples cited above do not provide any features to prevent shrinkage along their length. The present invention provides features to anchor itself to the slabs it separates all along its length as well as providing anchoring features to preclude pull-out. Additionally, the features which preclude pull-out also act as water and weed intrusion barriers.
In summary, prior art fails to address several key issues in the mechanical attachment of the cover to the concrete, resulting in a weakened slab or dependence on the presence of the forms for structural integrity. Prior art additionally fails to recognize effects that may only be manifested several years after installation, such as shrinkage of the compliant cover or gapping due to slab motion.